Biosensor devices based on nanomechanical motion of microcantilevers comprise an emerging sensor platform. Molecular adsorption on a resonating microcantilever shifts its resonance frequency; resonance shifts are correlated with changes in cantilever mass. Another more sensitive detection mode relies on changes in surface stress. Interaction of analytes with molecules tethered to one surface of the cantilevers induces differential surface stress that causes cantilever bending. High selectivity in response is achievable through incorporation of biomolecular recognition elements into thin film coatings on the cantilever. The long-range goal of this research is to develop a revolutionary microcantilever platform technology for sensing applications requiring sensitive, specific, quantitative and multiplexed detection of airborne or fluid-borne analytes. The immediate goal of the proposed R21/R33 project is to develop a plastic microcantilever platform technology for sensitive, specific, quantitative, multiplexed, and label-free detection of proteins present in complex mixtures. Currently, the AFM cantilevers are used in sensing applications. Their dimensions and mechanical properties are far from optimal for sensing applications. We envision a revolutionary approach to fabricating microcantilevers specifically designed for sensing applications. We propose fabrication of arrays of plastic microcantilevers using low cost, high yield injection micromolding methods. The inherent advantages of this method include the ease with which the properties of the cantilever can be tuned to meet its intended application and significantly reduced fabrication costs (materials, tooling and labor). Our specific aims are focused on exploring injection micromolding methods for fabricating plastic microcantilevers, optimizing their cantilever design, and developing plastic microcantilever-based immunoassays.